You'll need a boot loader on the boot drive - unless your BIOS will allow you to boot from differing hard drives.
So yes, you can put XP on one, Linux on the other, but you'll probably need a boot loader to be able to do it. The Red Hat installer will do this for ya. It will keep the OS that you have in place and then install Linux to another partion or physical drive. Tread carefully in setup...if fu, your first OS is toast...